1. Technical Field
The present invention relates generally to Ball Grid Array (hereinafter “BGA”) packages. In particular, the present invention relates to the use of partially captured interconnections, wherein the uncaptured region is selectively oriented in the direction of the highest stress within the BGA package.
2. Related Art
In the manufacture of BGA packages, thermal mismatch between the chip module and the printed circuit board may produce fatigue failure of the BGA interconnections, or solder joints. One solution for this problem is the elongation of the solder joints, which increases the compliance of the solder joints, thereby increasing the fatigue life of the BGA package. Solder joints have been elongated by the use of “captured pads” which form mask-defined solder joints. Along with increasing the height of the solder joint, the use of captured pads enhances the adhesion of the pads to the underlying chip module or printed circuit board. Unfortunately, stress concentrations within mask-defined solder joints tends to decrease the fatigue life of the solder joints. Alternative techniques employed to elongate the solder joints and increase fatigue life include the use of spacers, high-melt solder columns, selective solder joints containing an excess solder volume, etc. However, many of these techniques reduce the amount of space on the printed circuit board available for wiring.
Accordingly, there exists a need in the industry for a BGA package having an increased fatigue life, without sacrificing wiring space.